1. Field of the Invention
The invention relates to a method for insect resistance management in agriculture applications. More particularly, this invention pertains to providing a refuge for pest insects adjacent to plantings of genetically modified plants that produce insecticidal proteins of Bacillus thuringiensis such as BT-cotton, BT-corn, and BT-potatoes (BT Crops), said refuge providing a method for delaying, or possibly preventing said pests from developing resistance to the Bacillus thuringiensis protein.
2. Background of the Technology
The introduction of transgenic cotton plants expressing endotoxin derived from Bacillus thuringiensis Berliner (BT cotton) has greatly aided producers in maintaining control of Heliothis virescens larvae (tobacco budworm) and Helicoverpa zea larvae (bollworm), although to a lesser degree. BT cotton plants provide season long expression of the insecticidal toxins which has raised concerns about resistance development.
According to a United States Environmental Protection Agency (EPA) and United States Department of Agriculture (USDA) position paper on Resistance Management1, the EPA and USDA “generally support the following strategy to manage the development of pest resistance to BT toxins expressed in crops. That is, a structured refuge/high dose strategy should be employed for susceptible pests within the current understanding of the technology. The presence of an effective structured refuge, in combination with a high dose expression level of the BT toxin, has the potential to delay the development of resistance in pests. Refuges are non-BT host plants that are managed to provide sufficient susceptible adult insects to mate with potential BT-resistant adult insects to dilute the frequency of resistance genes. The 1998 SAP subpanel on BT crop resistance management suggested that production of 500 susceptible adults in the refuge should be available for mating with every potentially resistant adult in a BT field (assuming a resistance allele frequency of 5×10−2) (Final Report of the Subpanel on Bacillus thuringiensis (BT) Plant-Pesticides and Resistance Management, February, 1998 (186 kb, PDF).1 Several strategies have been discussed (Fischoff 1992, McGaughey and Whalon 21992, Mallet and Porter 1992, Caprio 1994), but the current strategy recommends the use of plants with high dose expression and the provision of an external refuge in close proximity to the transgenic plants (ILSI HESI 1998). Under the current strategy, producers using the BT cotton technology are allowed two possible options (S. Matten 2000). 1) For every 100 acres, Non-BT cotton must be planted on 20% of the acreage within one mile of the transgenic field, and the non-BT cotton may be treated with insecticides except for BT insecticide products. 2) For every 100 acres, Non-BT cotton must be planted on 3.8% of the acreage with in one mile from BT fields, but the refuge cannot be treated with any insecticide having activity on lepidopteran larvae. Non-BT cotton has been adopted as the refuge because it will be temporarily similar to the BT cotton and can serve as a refuge for the entire cotton production season. This option was subsequently revised (IRM Guide 2002) to provide a 5% unsprayed refuge instead of 3.8%.
Other hosts for Heliothis virescens and Helicoverpa zea have been reported (Quaintance and Brues 1905, Snow and Brazzel 1965, Snow et al. 1966, Stadelbacher et al. 1986), but many of these hosts are short lived. Other studies have explored the possibility of planting identified hosts to serve as a refuge for BT cotton, but these planting were comprised mainly of plants considered weeds in the cotton production system (Craig et al. 1999). Although the concept of using such plants as a refuge is valid, it would be easier to promote using alternative refuge plants that are not considered weed species. Paulownia was reported as a host of Heliothis virescens in a graduate student dissertation (Parker 2000), but the production of larvae per acre was not considered to be sufficient for refuge use.
Paulownia is a rapid growing tree introduced to the United States from China over 150 years ago (Kays et al. 1997). There are several species but Paulownia tomentosa is probably the most widespread. Others include Paulownia elongata, Paulownia fortunei, and Paulownia catalpafolia. Paulownia has a sparse distribution across the cotton belt, but in recent years has become an interest of some tree production farms. Parker (2000) reported that the plant spacing required for the tree production limited the per acre production of larvae although larvae were utilizing the paulownia for the entire cotton production season.
What is needed in the cotton farming industry is a refuge crop that will provide adequate refuge for Heliothis virescens larvae and Helicoverpa zea larvae and other cotton pests without requiring cotton farmers to sacrifice part of their yield or a large portion of valuable agricultural land.